Field-effect transistor and method for the fabrication thereof

1. Field-effect transistor having at least one channel layer, said channel layer comprising a group-III-nitride compound semiconductor, wherein the field-effect transistor comprises at least one source electrode and at least one drain electrode, with the at least one source electrode and the at least one drain electrode each having at least one contact, with the at least one contact having a same or smaller depth than the channel layer;

said source electrode and drain electrode comprising at least one doped region extending from the same surface into the at least one channel layer, wherein the depth of penetration of said doped region is selected from approximately 10 nm to approximately 200 nm, and a depth of penetration is equal or smaller than a channel depth, and the gradient of the dopant concentration at the lower interface between the channel layer and the doped region is smaller than 14 nm/decade.

2. Field-effect transistor according to claim 1 , wherein the depth of penetration of said doped region is selected from approximately 10 nm to approximately 30 nm.

3. Field effect transistor according to claim 1 , wherein the gradient of the dopant concentration at least at the lower interface between the channel layer and the doped region is smaller than 8 nm/decade.

4. Field effect transistor according to claim 1 , wherein the dopant is selecteed from the group comprising magnesium and/or silicon.

5. Field effect transistor according to claim 1 , wherein the channel layer comprises at least one first sublayer and at least one second sublayer, wherein said first and second sublayers each comprise an group-III-nitride compound semiconductor of different composition.

6. Field-effect transistor having at least one channel layer, said channel layer comprising a group-III-nitride compound semiconductor, wherein the compound semiconductor comprises at least one element from the chemical group III being selected from any of gallium, aluminium, indium and/or boron and wherein the compound semiconductor comprises further at least nitrogen, wherein the field-effect transistor comprises at least one source electrode and at least one drain electrode, with the at least one source electrode and the at least one drain electrode each having at least one contact, with the at least one contact having a same or smaller depth than the channel layer, said source electrode and drain electrode comprising at least one doped region extending from the same surface into the at least one channel layer, wherein the dopant is selected from the group comprising magnesium and/or silicon and the depth of penetration of said doped region is selected from approximately 10 nm to approximately 200 nm, and the gradient of the dopant concentration at the lower interface between the channel layer and the doped region is smaller than 14 nm/decade.

7. Field-effect transistor according to claim 6 , wherein the depth of penetration of said doped region is selected from approximately 10 nm to approximately 30 nm.

8. Field effect transistor according to claim 6 , wherein the gradient of the dopant concentration at least at the lower interface between the channel layer and the doped region is smaller than 8 nm/decade.

9. Field effect transistor according to claim 6 , wherein the channel layer comprises at least one first sublayer and at least one second sublayer, wherein said first and second sublayers each comprise an group-III-nitride compound semiconductor of different composition.

10. A method for manufacturing a field effect transistor having at least one channel layer, said channel layer comprising a group-III-nitride compound semiconductor, said method comprising at least the steps of providing a substrate;

depositing the at least one channel layer from a compound semiconductor onto a first surface of the substrate by means of MOCVD, wherein the compound semiconductor comprises at least one element from the chemical group III being selected from any of gallium, aluminium, indium and/or boron and wherein the compound semiconductor comprises further at least one element from the chemical group V being selected from nitrogen, phosphorous and/or arsenic, wherein the compound semiconductor comprises at least nitrogen;

producing any of at least one source electrode and/or at least one drain electrode by forming at least one doped region extending from the first surface into the at least one channel layer, with the at least one source electrode and the at least one drain electrode each having at least one contact, with the at least one contact having a same or smaller depth than the channel layer;

wherein the depth of penetration of said doped region is selected from approximately 10 nm to approximately 200 nm, such that the gradient of the dopant concentration at the lower interface between the channel layer and the doped region is smaller than 14 nm/decade.

11. Method according to claim 10 , wherein the depth of penetration of said doped region is selected from approximately 10 nm to approximately 30 nm.

12. Method according to claim 10 , wherein the dopant is supplied into the doped region from the gas phase during the fabrication of the at least one channel layer.

13. Method according to claim 10 , wherein the dopant is implanted into the at least one layer.

14. Method according to claim 10 , wherein the channel layer is tempered at a temperature between approximately 970° C. and approximately 1050° C.

15. Method according to claim 10 , wherein the channel layer is tempered at a temperature between approximately 970° C. and approximately 1030° C.

16. Method according to claim 10 , wherein the dopant is selecteed from the group comprising magnesium and/or silicon.

17. Method according to claim 10 , wherein the channel layer comprises at least one first sublayer and at least one second sublayer, wherein said first and second sublayers each comprise an group-III-nitride compound semiconductor of different composition and the interface forms a diffusion barrier for the dopant.